Method for the making soldering flux and resulting weld joint

Abstract

To improve the resistance of a solder to strains, especial thermal strains, superelastic particles are incorporated into the solder in a proportion by volume of 10 to 30% approximately. So that this incorporation can be done, the particles are coated with a metal, for example copper, that is wettable by the solder.

What is claimed is:  
     
       1. A solder paste including 
       a matrix comprising a metal solder; and  
       particles distributed substantially homogeneously in the matrix, wherein  
       the particles comprise a superelastic alloy;  
       the particles are coated with a metal coating; and  
       the metal coating is wettable by the metal solder.  
     
     
       2. The solder paste according to  claim 1 , wherein the particles are substantially spherical and have a diameter of about 1 to 50 μm. 
     
     
       3. The solder paste according to  claim 1 , wherein the particles represent about 5 to 30% of the total volume of the paste. 
     
     
       4. The solder paste according to  claim 1 , wherein the superelastic alloy is a shape memory alloy. 
     
     
       5. The solder paste according to  claim 4 , wherein the shape memory alloy contains Ni and Ti; Cu, Zn and Al; or Cu, Al and Ni. 
     
     
       6. The solder paste according to  claim 1 , wherein the metal coating comprises a metal selected from the group consisting of Cu, Ni, Au, Sn, Ag and Pb. 
     
     
       7. The solder paste according to  claim 6 , wherein the metal coating has a thickness of about 1 μm or less. 
     
     
       8. A method of making the solder paste of  claim 1 , the method comprising 
       providing particles comprising a superelastic alloy;  
       coating the particles with a metal coating to form coated particles; and  
       incorporating the coated particles in a matrix comprising a metal solder, wherein  
       the metal coating is wettable by the metal solder.  
     
     
       9. The method according to  claim 8 , wherein the coating comprises depositing the metal coating on the particles in a chemical bath. 
     
     
       10. The method according to  claim 9 , wherein the surface of the particles is sensitized by the formation of metal aggregates. 
     
     
       11. The method according to  claim 10 , wherein the aggregates are based on Sn—Pd, and formed by chemical deposition in corresponding chloride baths. 
     
     
       12. The method according to  claim 8 , wherein the coating comprises electrolytically depositing the metal coating on the particles. 
     
     
       13. The method according to  claim 8 , further comprising, before the incorporating step, coating the coated particles with a flux. 
     
     
       14. The method according to  claim 8 , wherein the particles have a substantially spherical shape with a diameter ranging from 1 to 50 μm approximately. 
     
     
       15. The method according to  claim 8 , wherein the metal coating has a thickness of less than about 1 μm. 
     
     
       16. The method according to  claim 8 , wherein the metal coating comprises a metal selected from the group consisting of Cu, Ni, Au, Sn, Ag and Pb. 
     
     
       17. The method according to  claim 8 , wherein the particles represent about 5% to 30% of the total volume of the paste. 
     
     
       18. The method according to  claim 8 , wherein the particles comprise an alloy selected from the group consisting of Ni—Ti, Cu—Zn—Al and Cu—Al—Ni. 
     
     
       19. The solder paste according to  claim 1 , wherein the particles are wettable by the metal coating.